The research will deal with the function of phagocytic cells in various types of reactions. Particular emphasis is to be given to three areas: 1) the intracellular mechanisms that permit certain microorganisms to survive within phagocytic vacuoles of phagocytes. The model system now under investigation is toxoplasma infection of mouse macrophages, and detailed studies are being made of the behavior of the lysosomal system in this interaction. 2) The role of macrophages in the induction of antibody response to sheep red cells by mouse spleen cells in vitro. When low concentrations of mercaptoethanol are added to the medium, apparently macrophages are no longer needed. Further studies will be made of the role of these cells, or of sulfhydryl reagents in this type of antibody formation. 3) Detailed study at the subcellular level of the mechanisms by which macrophages process iron-rich materials they have engulfed, then synthesize the iron-rich storage protein, ferritin, and on the storage of ferritin and ultimate delivery of iron for reuse by the body.